The invention relates to television systems in which an image of a picture may be displayed on an imaging display device having a viewing aspect ratio different from that of a conventional imaging display device.
In a typicel conventional television system, the ratio of the picture width to its height at the display device is 4:3. This ratio is called the aspect ratio. Recently, there has been an interest in using wider aspect ratios for television systems such as 2:1 or 5:3 ratios, which more nearly equal the ratio of width to height that is viewed by the human eye. The 5:3 aspect ratio has received particular attention since release prints for motion pictures film in the United States employ this ratio and thus the pictures of such prints may be transmitted and received without cropping. It may be desirable that a television system adapted to send and receive an extended aspect ratio picture be also compatible with a conventional system in which the picture information has a 4:3 aspect ratio.
Furthermore, it may be desirable to display a picture having the conventional aspect ratio on a screen of an extended aspect ratio receiver without suffering degradation of the sharpness of the picture or increased noise content, particularly in an area of the display where either a picture with the extended aspect ratio or a picture with the conventional aspect ratio may be displayed.
It may be also desirable to display a video signal containing extended aspect ratio picture information in a receiver having a conventional aspect ratio display by displaying only that portion of the picture which may fit its display. Such television receiver may be required to extract timing information, as provided by the horizontal sync pulses, for example, from the signal containing extended aspect ratio picture information.
In a conventional television system, a displayed video signal of each scan line is sent during a predefined portion of scan line time. For example, in the NTSC system, the displayed video signal is sent during a 52.6 microseconds period of a scan line time. Conventionally, the displayed video signal is displayed on the screen at the same rate in which it is received. That portion of the scan period not occupied by the displayed video signal, called the blanking period, is utilized for sending a sync signal such as the horizontal sync, and also a color burst signal, where applicable. According to the NTSC standard, the blanking period occupies 10.9 microseconds out of 63.5 microseconds of a scan line time.
The NTSC standard defines the bandwidth of the transmitted video signal and the scanning frequency. The bandwidth and the scanning frequency determine, to a great extent, the sharpness of picture details along a scan line.
One feature of the invention is a television system with an extended aspect ratio capability in which the scanning frequency of the conventional television system may be maintained.
Another feature of the invention is a television system in which the bandwidth required to transmit and receive video information for a picture having extended aspect ratio need not be increased in comparison with that of the conventional television system.
One aspect of the invention is a provision, used with a conventional aspect ratio television receiver for displaying a picture having an extended aspect ratio, by cropping out a portion of the picture so that the remaining portion of the picture is adapted for display without suffering dimensional distortions.
Another aspect of the invention is a provision, used with a television receiver capable of displaying an extended aspect ratio picture for displaying a conventional television signal without suffering dimensional distortions.